1. Field of the Invention
This invention relates to aerial cable installations and aerial suspension devices therefor.
2. Description of the Related Art
It is known to provide aerial cable installations comprising an aerial cable suspended from a plurality of spaced apart suspension points provided on poles, towers and like upstanding supports. Typically the cable is suspended from the suspension points through respective suspension devices each of which comprises a clamp provided with a suspension eye and comprising two saddle members engaging the cable on diametrically opposite sides thereof and bolted together. One of the functions of the clamp is to apply a clamping force to the cable which allows slippage of the cable through the clamp when the cable is subjected to an unbalanced load in the cable spans immediately adjacent the clamp to reduce this imbalance. The clamping is compression force and the coefficient of friction between the contacting surfaces of the cable and clamp determine the frictional force opposing slippage due to an unbalanced load in the cable spans immediately adjacent the clamp and in a prior art clamp as shown in FIG. 4 of the accompanying drawings the clamping compression force is adjusted during installation by using spacers of a selected thickness (for example 3.3 mm) between the saddle members. In the illustrated prior art clamp 1, which is obtainable from Dulmison of Corby, Northants, England, two saddle members 2 and 3 engage the cable 4 on diametrically opposite sides thereof and are bolted together by respective nut and bolt fastener assemblies 5 which pass through aligned holes in flanges 6 and 7 of the saddle members 2 and 3 with respective spacers 8, in the form of washers, positioned between the flanges 6 and 7. The nut and bolt assemblies 5 are tightened until the flanges 6 and 7 engage with the spacers 8. As will be appreciated the spacers limit further movement of the saddle members towards each other and for a given torque applied to the bolts which bolt the saddle members and spacers together the clamping compression force applied to the cable and thus the frictional force opposing slippage will depend on the actual diameter of the cable and the thickness of the spacers.
We have discovered that the above-described clamp, whilst suitable for use with metallic cables having relatively close tolerance outer diameters (for example ±3%), is not particularly suitable for use with cables such as all-dielectric self-supporting (ADSS) cables which have relatively large tolerance outer diameters (for example ±5%) since the variation in the diameter of a latter cable along its length results in a variation of the force opposing slippage depending upon the actual cable diameter at the location of the clamp along the length of the cable. This problem of diameter variation is exacerbated because an ADSS cable is more compressible than a metallic cable and also requires reinforcing rods to be wound about the cable at the clamping location thereby introducing a further tolerance on the cable diameter.
An object of one aspect of the invention is to avoid dependence of the clamping force and thus the force opposing slippage of the cable in the clamp on the actual diameter of the cable at the location of the clamp.